Methods for production of organochlorosilanes are well known in the art. One such method used to produce an organochlorosilane is by reacting a chlorosilane of the formula R.sub.a Cl.sub.(3-a) SiH with unsaturated olefinic material in the presence of a platinum catalyst wherein R is independently selected from the hydrogen atom, an alkyl group containing 1 to 6 carbons, and an aryl group containing 6 to 10 carbons and a has the value of 0 to 2. The organoalkoxysilane is then produced by the alkoxylation (reaction with an alcohol) of the organochlorosilane with hydrochloric acid being produced as a by-product.
The alkoxylation of acrylate functional chlorosilanes, in particular, is difficult due to numerous side reactions that can occur. These side reactions can occur because of the reaction conditions, reaction of the by-products or impurities, or instability of the acrylate group from undergoing polymerization. These side reactions can result in the formation of methyl chloride, methyl methacrylate, other toxic materials, and high molecular weight polymers or gels. Other organochlorosilanes can be difficult to alkoxylate because of reactive or sensitive organofunctional groups that react or decompose in the presence of certain process conditions.
During alkoxylation of organoalkoxysilanes it is essential to remove the HCl by-product to prevent many of the possible side reactions and product contamination. High temperatures, in conjunction with some contaminants, can also be disastrous.
Methods of alkoxylation known in the art include the use of batch and continuous processes. Although batch processing is applicable for making alkoxysilanes, the use of a solvent, higher temperatures, or an acid acceptor may be required to ensure complete separation of the HCl from the product or to minimize the contact time between the HCl and the product. Although these process aides can be applied to continuous processes, operation without them is possible. Because of this it is preferred that the materials be made in a continuous manner.
Methods for alkoxylation of chlorosilanes are well known in the art. However, many of these methods are not applicable to the production of acryloxyorganoalkoxysilanes or organoalkoxysilanes as their operating parameters could result in side reactions, by product formation or gels. For example, Kotzsch et al., U.S. Pat. No. 4,039.567, teaches a continuous method for making alkoxysilanes in which the chlorosilane and alcohol are fed in liquid form and in stoichiometric amounts. This method requires that the reaction mixture be maintained at its boiling point. Because of higher boiling points of most organoalkoxysilanes numerous side reactions would occur if sensitive materials were employed in this method.
Hallgren, U.S. Pat. No. 4,471,133, also teaches a similar method to that of Kotzsch, however, the silane is fed only in the vapor form and alkoxylation of only a limited number of organoalkoxysilanes are taught. Again, the heat required to vaporize the silane could result in side reactions if reactive organochlorosilanes were employed in this method.
Another method for alkoxylation of organochlorosilanes is taught by Nitzsche et al. in U.S. Pat. No. 3,792,071. This method comprises a one column system in which the chlorosilane is fed in the liquid form and any alcohol is fed in a gaseous (vaporized) state. An excess of the alcohol is initially fed to create reflux in the head of the column followed by the feeding of only amounts necessary to achieve a complete reaction. To maintain the reflux the column must be heated or higher temperatures must be obtained in the reboiler.
Several other continuous methods for the production of organoalkoxysilanes are known in the art. One such method uses a two reactor system as described by Schinabeck et al., U.S. Pat. No. 4,298,753. The first reactor, a stirred vessel or tube type, is used to partially react the chlorosilane while the second reactor, a fractional distillation type, is used to complete the reaction. Because the HCl is in contact with the material in the first reactor the probability of side reactions occurring appears to be high although it appears that this is reduced by cooling the first reactor. It is also vague as to how and to what extent the HCl is removed prior to its introduction into the second reactor where higher temperatures are necessitated to complete the reaction.
Fischer et al., U.S. Pat. No. 4,506,087, teaches another two reactor system. In this system, the alcohol is fed into the second reactor and the unreacted amount is condensed and recycled into the first reactor. Again the HCl is not immediately removed from the reaction mixture in the first reactor.
It is an object of this invention to provide a method for producing organoalkoxysilanes by the alkoxylation of organochlorosilanes.
It is further an object of this invention to provide a method for producing organoalkoxysilanes in which the formation of gels and undesirable impurities is minimized through raw materials, process conditions and process equipment.
It is further an object of this invention to provide a continuous method for producing organoalkoxysilanes in which only one reactor is required.
It is further an object of this invention to provide a method for removing or reducing hydrolyzable chloride and other acids in the organoalkoxysilanes.